1. Field of the Invention
The present invention relates to a method for manufacturing a metal-oxide semiconductor sensor, and more particularly to a method for manufacturing a metal-oxide semiconductor sensor having a more oxide layer.
2. Description of the Prior Art
For manufacturing a metal-oxide semiconductor sensor, a protective layer for preventing the inter-metal dielectric layer, IMD layer, from plasma damage to reduce dark current is formed on the inter-metal dielectric layer.
As shown in FIG. 1A, a semiconductor structure 100 including elements, e.g. a source, a gate, a drain, etc., of a MOS sensor is provided, wherein the elements of the MOS are not shown in FIG. 1A. A plurality of conductors 102 is applied on the semiconductor structure 100, wherein there is only a conductor 102 shown in FIG. 1A. An inter-metal dielectric layer 104, IMD layer, is deposited onto the conductors 102. The IMD layer 104 may cover portions of the semiconductor structure 100 that are not covered by conductors 102. A protective layer 106 is formed onto the IMD layer 104 to prevent the damage from plasma and to reduce the dark current.
As shown in FIG. 1B, the protective layer 106 and the IMD layer 104 is subsequently etched after patterning the protective layer 106. After the etching step, via holes 108 are formed inside the protective layer 106 and the IMD layer 104 and on portions of the conductors 102 to expose the surfaces of the exposed conductors 102. As shown in FIG. 1C, a cleaning step cleans the protective layer 106 and the exposed conductors 102 before forming a glue layer onto the protective layer 106 of the MOS sensor, wherein the glue layer is not shown in FIG. 1C. After the cleaning step, the cleaned protective layer 106 becomes thinner, wherein a plurality of particles composed of the material of the protective layer 106 are formed.
As shown in FIG. 1D, the MOS sensor is moved into a process-chamber 110 before the cleaning step. The process chamber 110 includes a bell jar 112 and a tank 114, wherein the process chamber 110 is covered by the bell jar 112. When the cleaning step cleans the protective layer 106 and the exposed conductors 102, a plurality of particles 106′ forms due to the thinning protective layer 106. The material of the produced particles 106′ and the material of the protective layer 106 are the same. The particles 106′ are adhered on the bell jar 112 to prevent the semiconductor structure 100, the elements on the semiconductor structure 100 and the whole MOS sensor from the particles 106′. The MOS sensor is removed from the process chamber 110 later.
If the particles 106′ adhered on the bell jar 112 drop on the MOS sensor, the MOS sensor may be broken due to the dropped particles 106′. The yield for manufacturing the MOS sensors is reduced due to the broken MOS sensors. To maintain the yield for manufacturing the MOS sensors, a new bell jar 112 replaces a used bell jar 112 filled with particles 106′ to prevent particles 106′ from dropping.
A new bell jar 112 replaces a used bell jar 112 after manufacturing the MOS sensors on about 1250–1500 pieces of wafers except CMOS sensors. When manufacturing CMOS sensors, a new bell jar 112 has to replace a used bell jar 112 after manufacturing the CMOS sensors on about 200–300 pieces of wafers. The cost of the bell jars 112 for manufacturing the CMOS sensors is much higher than the cost of the bell jars 112 for manufacturing the other kinds of MOS sensors because of changing the bell jar 112. The preventive maintenance period for changing a bell jar 112 for manufacturing the CMOS sensors is much shorter than the preventive maintenance period for changing a bell jar 112 for manufacturing the other kinds of MOS sensors.
A prior method for reducing the cost and increasing the preventive maintenance period for manufacturing the CMOS sensors is to coat a ceramic layer on the bell jar 112 to rough the surface of the bell jar 112 for adhering more particles 106′ produced by the cleaned protective layer 106. Even if the bell jar 112 having a rougher surface does adhere little more particles 106′, the improvement due to the ceramic layer is still not good enough. The cost for manufacturing the CMOS sensors is still higher than the cost for manufacturing the other kinds of the MOS sensors. The preventive maintenance period for manufacturing the CMOS sensors is still shorter than the preventive maintenance period for manufacturing the other kinds of the MOS sensors. The efficiency for manufacturing the CMOS sensors by the prior improved method is not enough.
According to the above description, it is necessary to develop a method to reduce the cost and increase the preventive maintenance period for manufacturing complementary metal-oxide semiconductor sensors.